Abstract: Twenty-two case of malignant melanoma (MM) were studied immunohistochemically for the presence of ferritin (FE),S100 protein and alpha-1-antichymotrypsin (AlAchy) by the double PAP method on routine formalin fixed and paraffin-embedded tissues.The formaldehyde-induced fluorescence (FIF) in MM was also observed.It was found that the positive rates of FE,S100 protein,A1Achy and FIF in these cases were 77.3%,95.5%,63.3% and 100% respectively.The findings suggest that:1.raised serum FE concentration in MM patients may be attri buted to the increase of FE synthesis in tumor cells,stromal reaction and non-specific response of mononu-clear phagocytic system;2.detection of S100 protein and FIF may help to distinguish poorly differentiated MM,especially the amelanotic type,from Pnget's disease of the skin and some tumors of obscure histogenetic origin.